1. Field of the Invention
The present invention relates to 3-dimensional structures and, more specifically, to supports for such structures. The present invention relates to structures having at least one dimension on the order of one micrometer, or even of a few tenths of a micrometer or less.
2. Discussion of the Related Art
To form 3-D structures, a method comprises using a substrate, for example, made of silicon, in which a great number of very narrow trenches, close to one another, for example at a step on the order of one micrometer, separated by thin silicon blades, are formed. Micro-electro-mechanical devices (MEMS) are thus for example formed. Various layers may also be arranged on the walls and bottom of these trenches to form electronic components. Fuel cell cores or cells forming micro-batteries may also be formed on the walls and the bottom of these trenches.
In the case of electronic components, capacitors or diodes having their active areas extending on the walls and bottom of the trenches are for example formed. Thus, capacitors having very high capacitances per surface unit are obtained.
FIG. 1 illustrates an example of a support for 3-D components. The support is formed of a substrate 1, for example, made of silicon, in which trenches 3 are formed. Trenches 3 have a significantly elongated rectangular shape, at the substrate surface. The trenches extend parallel to one another. Thus, each trench 3 is separated from another trench by a silicon blade 4.
FIG. 2 illustrates a partial cross-section view of a capacitor formed on a support such as that in FIG. 1. In FIG. 2, only two trenches 3 are shown.
A stack of a first conductive layer 6 and of an insulating layer 7 extends on the surface of substrate 1 and on the walls and bottom of trenches 3. A second conductive layer 9 fills the space remaining in trenches 3 and extends, above the substrate, on insulating layer 7. Conductive layers 6 and 9 form the two capacitor electrodes. Contacts, not shown, are taken in appropriate fashion on each of these electrodes.
The capacitance of the capacitor of FIG. 2 is linked to the facing surface between each of electrodes 5 and 9, and to the thickness of insulating layer 7. A recurrent object in the forming of 3-D capacitors is to increase their capacitances without increasing the surface area that they take up at the substrate surface. The facing surface between electrodes is thus desired to be increased. For this purpose, it is desirable to increase height h and to decrease thickness e of the blades between trenches to form more trenches per area unit.
However, when it is dug too deeply or when very close trenches are formed, mechanical stress that may deform the blades and the trenches appears on each of the blades separating the trenches. This limits the increase of the ratio of the trench depth to the blade thickness.